WebSVN – HomeAutomation – Diff – /trunk/PcSoftware/Atom/Daemon.py


"""Disk And Execution MONitor (Daemon)
 
Configurable daemon behaviors:
 
   1.) The current working directory set to the "/" directory.
   2.) The current file creation mode mask set to 0.
   3.) Close all open files (1024).
   4.) Redirect standard I/O streams to "/dev/null".
 
A failed call to fork() now raises an exception.
 
References:
   1) Advanced Programming in the Unix Environment: W. Richard Stevens
   2) Unix Programming Frequently Asked Questions:
         http://www.erlenstar.demon.co.uk/unix/faq_toc.html
"""
 
__author__ = "Chad J. Schroeder"
__copyright__ = "Copyright (C) 2005 Chad J. Schroeder"
 
__revision__ = "$Id$"
__version__ = "0.2"
 
# Standard Python modules.
import os               # Miscellaneous OS interfaces.
import sys              # System-specific parameters and functions.
import Settings
 
# Default daemon parameters.
# File mode creation mask of the daemon.
UMASK = 0
 
# Default working directory for the daemon.
WORKDIR = "/"
 
# Default maximum for the number of available file descriptors.
MAXFD = 1024
 
# The standard I/O file descriptors are redirected to /dev/null by default.
if (hasattr(os, "devnull")):
   REDIRECT_TO = os.devnull
else:
   REDIRECT_TO = "/dev/null"
 
def createDaemon():
   """Detach a process from the controlling terminal and run it in the
   background as a daemon.
   """
 
   try:
      # Fork a child process so the parent can exit.  This returns control to
      # the command-line or shell.  It also guarantees that the child will not
      # be a process group leader, since the child receives a new process ID
      # and inherits the parent's process group ID.  This step is required
      # to insure that the next call to os.setsid is successful.
      pid = os.fork()
   except (KeyboardInterrupt, SystemExit):
      raise
   except OSError, e:
      raise Exception, "%s [%d]" % (e.strerror, e.errno)
 
   if (pid == 0):   # The first child.
      # To become the session leader of this new session and the process group
      # leader of the new process group, we call os.setsid().  The process is
      # also guaranteed not to have a controlling terminal.
      os.setsid()
 
      # Is ignoring SIGHUP necessary?
      #
      # It's often suggested that the SIGHUP signal should be ignored before
      # the second fork to avoid premature termination of the process.  The
      # reason is that when the first child terminates, all processes, e.g.
      # the second child, in the orphaned group will be sent a SIGHUP.
      #
      # "However, as part of the session management system, there are exactly
      # two cases where SIGHUP is sent on the death of a process:
      #
      #   1) When the process that dies is the session leader of a session that
      #      is attached to a terminal device, SIGHUP is sent to all processes
      #      in the foreground process group of that terminal device.
      #   2) When the death of a process causes a process group to become
      #      orphaned, and one or more processes in the orphaned group are
      #      stopped, then SIGHUP and SIGCONT are sent to all members of the
      #      orphaned group." [2]
      #
      # The first case can be ignored since the child is guaranteed not to have
      # a controlling terminal.  The second case isn't so easy to dismiss.
      # The process group is orphaned when the first child terminates and
      # POSIX.1 requires that every STOPPED process in an orphaned process
      # group be sent a SIGHUP signal followed by a SIGCONT signal.  Since the
      # second child is not STOPPED though, we can safely forego ignoring the
      # SIGHUP signal.  In any case, there are no ill-effects if it is ignored.
      #
      # import signal           # Set handlers for asynchronous events.
      # signal.signal(signal.SIGHUP, signal.SIG_IGN)
 
      try:
         # Fork a second child and exit immediately to prevent zombies.  This
         # causes the second child process to be orphaned, making the init
         # process responsible for its cleanup.  And, since the first child is
         # a session leader without a controlling terminal, it's possible for
         # it to acquire one by opening a terminal in the future (System V-
         # based systems).  This second fork guarantees that the child is no
         # longer a session leader, preventing the daemon from ever acquiring
         # a controlling terminal.
         pid = os.fork()    # Fork a second child.
      except (KeyboardInterrupt, SystemExit):
         raise
      except OSError, e:
         raise Exception, "%s [%d]" % (e.strerror, e.errno)
 
      if (pid == 0):    # The second child.
         # Since the current working directory may be a mounted filesystem, we
         # avoid the issue of not being able to unmount the filesystem at
         # shutdown time by changing it to the root directory.
         os.chdir(WORKDIR)
         # We probably don't want the file mode creation mask inherited from
         # the parent, so we give the child complete control over permissions.
         os.umask(UMASK)
      else:
         # exit() or _exit()?  See below.
         os._exit(0)    # Exit parent (the first child) of the second child.
   else:
      # exit() or _exit()?
      # _exit is like exit(), but it doesn't call any functions registered
      # with atexit (and on_exit) or any registered signal handlers.  It also
      # closes any open file descriptors.  Using exit() may cause all stdio
      # streams to be flushed twice and any temporary files may be unexpectedly
      # removed.  It's therefore recommended that child branches of a fork()
      # and the parent branch(es) of a daemon use _exit().
      os._exit(0)   # Exit parent of the first child.
 
   # Close all open file descriptors.  This prevents the child from keeping
   # open any file descriptors inherited from the parent.  There is a variety
   # of methods to accomplish this task.  Three are listed below.
   #
   # Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum
   # number of open file descriptors to close.  If it doesn't exists, use
   # the default value (configurable).
   #
   # try:
   #    maxfd = os.sysconf("SC_OPEN_MAX")
   # except (AttributeError, ValueError):
   #    maxfd = MAXFD
   #
   # OR
   #
   # if (os.sysconf_names.has_key("SC_OPEN_MAX")):
   #    maxfd = os.sysconf("SC_OPEN_MAX")
   # else:
   #    maxfd = MAXFD
   #
   # OR
   #
   # Use the getrlimit method to retrieve the maximum file descriptor number
   # that can be opened by this process.  If there is not limit on the
   # resource, use the default value.
   #
   import resource      # Resource usage information.
   maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
   if (maxfd == resource.RLIM_INFINITY):
      maxfd = MAXFD
 
   # Iterate through and close all file descriptors.
   for fd in range(0, maxfd):
      try:
         os.close(fd)
      except (KeyboardInterrupt, SystemExit):
         raise
      except OSError:   # ERROR, fd wasn't open to begin with (ignored)
         pass
 
   # Redirect the standard I/O file descriptors to the specified file.  Since
   # the daemon has no controlling terminal, most daemons redirect stdin,
   # stdout, and stderr to /dev/null.  This is done to prevent side-effects
   # from reads and writes to the standard I/O file descriptors.
 
   os.open(Settings.Settings["LOGPATH"], os.O_CREAT|os.O_APPEND|os.O_RDONLY) # stdin 
   os.open(Settings.Settings["LOGPATH"], os.O_CREAT|os.O_APPEND|os.O_RDWR)   # stdout
   os.open(Settings.Settings["LOGPATH"], os.O_CREAT|os.O_APPEND|os.O_RDWR)   # stderr
 
   # This call to open is guaranteed to return the lowest file descriptor,
   # which will be 0 (stdin), since it was closed above.
   #os.open(REDIRECT_TO, os.O_RDWR) # standard input (0)
 
   # Duplicate standard input to standard output and standard error.
   #os.dup2(0, 1)           # standard output (1)
   #os.dup2(0, 2)           # standard error (2)
 
   return(0)
 

Subversion Repositories HomeAutomation

(root)/trunk/PcSoftware/Atom/Daemon.py @ 875 – Rev 856 → 869

Rev 856		Rev 869
1	"""Disk And Execution MONitor (Daemon)	1	"""Disk And Execution MONitor (Daemon)
2		2
3	Configurable daemon behaviors:	3	Configurable daemon behaviors:
4		4
5	1.) The current working directory set to the "/" directory.	5	1.) The current working directory set to the "/" directory.
6	2.) The current file creation mode mask set to 0.	6	2.) The current file creation mode mask set to 0.
7	3.) Close all open files (1024).	7	3.) Close all open files (1024).
8	4.) Redirect standard I/O streams to "/dev/null".	8	4.) Redirect standard I/O streams to "/dev/null".
9		9
10	A failed call to fork() now raises an exception.	10	A failed call to fork() now raises an exception.
11		11
12	References:	12	References:
13	1) Advanced Programming in the Unix Environment: W. Richard Stevens	13	1) Advanced Programming in the Unix Environment: W. Richard Stevens
14	2) Unix Programming Frequently Asked Questions:	14	2) Unix Programming Frequently Asked Questions:
15	http://www.erlenstar.demon.co.uk/unix/faq_toc.html	15	http://www.erlenstar.demon.co.uk/unix/faq_toc.html
16	"""	16	"""
17		17
18	__author__ = "Chad J. Schroeder"	18	__author__ = "Chad J. Schroeder"
19	__copyright__ = "Copyright (C) 2005 Chad J. Schroeder"	19	__copyright__ = "Copyright (C) 2005 Chad J. Schroeder"
20		20
21	__revision__ = "$Id$"	21	__revision__ = "$Id$"
22	__version__ = "0.2"	22	__version__ = "0.2"
23		23
24	# Standard Python modules.	24	# Standard Python modules.
25	import os # Miscellaneous OS interfaces.	25	import os # Miscellaneous OS interfaces.
26	import sys # System-specific parameters and functions.	26	import sys # System-specific parameters and functions.
27	import Settings	27	import Settings
28		28
29	# Default daemon parameters.	29	# Default daemon parameters.
30	# File mode creation mask of the daemon.	30	# File mode creation mask of the daemon.
31	UMASK = 0	31	UMASK = 0
32		32
33	# Default working directory for the daemon.	33	# Default working directory for the daemon.
34	WORKDIR = "/"	34	WORKDIR = "/"
35		35
36	# Default maximum for the number of available file descriptors.	36	# Default maximum for the number of available file descriptors.
37	MAXFD = 1024	37	MAXFD = 1024
38		38
39	# The standard I/O file descriptors are redirected to /dev/null by default.	39	# The standard I/O file descriptors are redirected to /dev/null by default.
40	if (hasattr(os, "devnull")):	40	if (hasattr(os, "devnull")):
41	REDIRECT_TO = os.devnull	41	REDIRECT_TO = os.devnull
42	else:	42	else:
43	REDIRECT_TO = "/dev/null"	43	REDIRECT_TO = "/dev/null"
44		44
45	def createDaemon():	45	def createDaemon():
46	"""Detach a process from the controlling terminal and run it in the	46	"""Detach a process from the controlling terminal and run it in the
47	background as a daemon.	47	background as a daemon.
48	"""	48	"""
49		49
50	try:	50	try:
51	# Fork a child process so the parent can exit. This returns control to	51	# Fork a child process so the parent can exit. This returns control to
52	# the command-line or shell. It also guarantees that the child will not	52	# the command-line or shell. It also guarantees that the child will not
53	# be a process group leader, since the child receives a new process ID	53	# be a process group leader, since the child receives a new process ID
54	# and inherits the parent's process group ID. This step is required	54	# and inherits the parent's process group ID. This step is required
55	# to insure that the next call to os.setsid is successful.	55	# to insure that the next call to os.setsid is successful.
56	pid = os.fork()	56	pid = os.fork()
57	except (KeyboardInterrupt, SystemExit):	57	except (KeyboardInterrupt, SystemExit):
58	raise	58	raise
59	except OSError, e:	59	except OSError, e:
60	raise Exception, "%s [%d]" % (e.strerror, e.errno)	60	raise Exception, "%s [%d]" % (e.strerror, e.errno)
61		61
62	if (pid == 0): # The first child.	62	if (pid == 0): # The first child.
63	# To become the session leader of this new session and the process group	63	# To become the session leader of this new session and the process group
64	# leader of the new process group, we call os.setsid(). The process is	64	# leader of the new process group, we call os.setsid(). The process is
65	# also guaranteed not to have a controlling terminal.	65	# also guaranteed not to have a controlling terminal.
66	os.setsid()	66	os.setsid()
67		67
68	# Is ignoring SIGHUP necessary?	68	# Is ignoring SIGHUP necessary?
69	#	69	#
70	# It's often suggested that the SIGHUP signal should be ignored before	70	# It's often suggested that the SIGHUP signal should be ignored before
71	# the second fork to avoid premature termination of the process. The	71	# the second fork to avoid premature termination of the process. The
72	# reason is that when the first child terminates, all processes, e.g.	72	# reason is that when the first child terminates, all processes, e.g.
73	# the second child, in the orphaned group will be sent a SIGHUP.	73	# the second child, in the orphaned group will be sent a SIGHUP.
74	#	74	#
75	# "However, as part of the session management system, there are exactly	75	# "However, as part of the session management system, there are exactly
76	# two cases where SIGHUP is sent on the death of a process:	76	# two cases where SIGHUP is sent on the death of a process:
77	#	77	#
78	# 1) When the process that dies is the session leader of a session that	78	# 1) When the process that dies is the session leader of a session that
79	# is attached to a terminal device, SIGHUP is sent to all processes	79	# is attached to a terminal device, SIGHUP is sent to all processes
80	# in the foreground process group of that terminal device.	80	# in the foreground process group of that terminal device.
81	# 2) When the death of a process causes a process group to become	81	# 2) When the death of a process causes a process group to become
82	# orphaned, and one or more processes in the orphaned group are	82	# orphaned, and one or more processes in the orphaned group are
83	# stopped, then SIGHUP and SIGCONT are sent to all members of the	83	# stopped, then SIGHUP and SIGCONT are sent to all members of the
84	# orphaned group." [2]	84	# orphaned group." [2]
85	#	85	#
86	# The first case can be ignored since the child is guaranteed not to have	86	# The first case can be ignored since the child is guaranteed not to have
87	# a controlling terminal. The second case isn't so easy to dismiss.	87	# a controlling terminal. The second case isn't so easy to dismiss.
88	# The process group is orphaned when the first child terminates and	88	# The process group is orphaned when the first child terminates and
89	# POSIX.1 requires that every STOPPED process in an orphaned process	89	# POSIX.1 requires that every STOPPED process in an orphaned process
90	# group be sent a SIGHUP signal followed by a SIGCONT signal. Since the	90	# group be sent a SIGHUP signal followed by a SIGCONT signal. Since the
91	# second child is not STOPPED though, we can safely forego ignoring the	91	# second child is not STOPPED though, we can safely forego ignoring the
92	# SIGHUP signal. In any case, there are no ill-effects if it is ignored.	92	# SIGHUP signal. In any case, there are no ill-effects if it is ignored.
93	#	93	#
94	# import signal # Set handlers for asynchronous events.	94	# import signal # Set handlers for asynchronous events.
95	# signal.signal(signal.SIGHUP, signal.SIG_IGN)	95	# signal.signal(signal.SIGHUP, signal.SIG_IGN)
96		96
97	try:	97	try:
98	# Fork a second child and exit immediately to prevent zombies. This	98	# Fork a second child and exit immediately to prevent zombies. This
99	# causes the second child process to be orphaned, making the init	99	# causes the second child process to be orphaned, making the init
100	# process responsible for its cleanup. And, since the first child is	100	# process responsible for its cleanup. And, since the first child is
101	# a session leader without a controlling terminal, it's possible for	101	# a session leader without a controlling terminal, it's possible for
102	# it to acquire one by opening a terminal in the future (System V-	102	# it to acquire one by opening a terminal in the future (System V-
103	# based systems). This second fork guarantees that the child is no	103	# based systems). This second fork guarantees that the child is no
104	# longer a session leader, preventing the daemon from ever acquiring	104	# longer a session leader, preventing the daemon from ever acquiring
105	# a controlling terminal.	105	# a controlling terminal.
106	pid = os.fork() # Fork a second child.	106	pid = os.fork() # Fork a second child.
107	except (KeyboardInterrupt, SystemExit):	107	except (KeyboardInterrupt, SystemExit):
108	raise	108	raise
109	except OSError, e:	109	except OSError, e:
110	raise Exception, "%s [%d]" % (e.strerror, e.errno)	110	raise Exception, "%s [%d]" % (e.strerror, e.errno)
111		111
112	if (pid == 0): # The second child.	112	if (pid == 0): # The second child.
113	# Since the current working directory may be a mounted filesystem, we	113	# Since the current working directory may be a mounted filesystem, we
114	# avoid the issue of not being able to unmount the filesystem at	114	# avoid the issue of not being able to unmount the filesystem at
115	# shutdown time by changing it to the root directory.	115	# shutdown time by changing it to the root directory.
116	os.chdir(WORKDIR)	116	os.chdir(WORKDIR)
117	# We probably don't want the file mode creation mask inherited from	117	# We probably don't want the file mode creation mask inherited from
118	# the parent, so we give the child complete control over permissions.	118	# the parent, so we give the child complete control over permissions.
119	os.umask(UMASK)	119	os.umask(UMASK)
120	else:	120	else:
121	# exit() or _exit()? See below.	121	# exit() or _exit()? See below.
122	os._exit(0) # Exit parent (the first child) of the second child.	122	os._exit(0) # Exit parent (the first child) of the second child.
123	else:	123	else:
124	# exit() or _exit()?	124	# exit() or _exit()?
125	# _exit is like exit(), but it doesn't call any functions registered	125	# _exit is like exit(), but it doesn't call any functions registered
126	# with atexit (and on_exit) or any registered signal handlers. It also	126	# with atexit (and on_exit) or any registered signal handlers. It also
127	# closes any open file descriptors. Using exit() may cause all stdio	127	# closes any open file descriptors. Using exit() may cause all stdio
128	# streams to be flushed twice and any temporary files may be unexpectedly	128	# streams to be flushed twice and any temporary files may be unexpectedly
129	# removed. It's therefore recommended that child branches of a fork()	129	# removed. It's therefore recommended that child branches of a fork()
130	# and the parent branch(es) of a daemon use _exit().	130	# and the parent branch(es) of a daemon use _exit().
131	os._exit(0) # Exit parent of the first child.	131	os._exit(0) # Exit parent of the first child.
132		132
133	# Close all open file descriptors. This prevents the child from keeping	133	# Close all open file descriptors. This prevents the child from keeping
134	# open any file descriptors inherited from the parent. There is a variety	134	# open any file descriptors inherited from the parent. There is a variety
135	# of methods to accomplish this task. Three are listed below.	135	# of methods to accomplish this task. Three are listed below.
136	#	136	#
137	# Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum	137	# Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum
138	# number of open file descriptors to close. If it doesn't exists, use	138	# number of open file descriptors to close. If it doesn't exists, use
139	# the default value (configurable).	139	# the default value (configurable).
140	#	140	#
141	# try:	141	# try:
142	# maxfd = os.sysconf("SC_OPEN_MAX")	142	# maxfd = os.sysconf("SC_OPEN_MAX")
143	# except (AttributeError, ValueError):	143	# except (AttributeError, ValueError):
144	# maxfd = MAXFD	144	# maxfd = MAXFD
145	#	145	#
146	# OR	146	# OR
147	#	147	#
148	# if (os.sysconf_names.has_key("SC_OPEN_MAX")):	148	# if (os.sysconf_names.has_key("SC_OPEN_MAX")):
149	# maxfd = os.sysconf("SC_OPEN_MAX")	149	# maxfd = os.sysconf("SC_OPEN_MAX")
150	# else:	150	# else:
151	# maxfd = MAXFD	151	# maxfd = MAXFD
152	#	152	#
153	# OR	153	# OR
154	#	154	#
155	# Use the getrlimit method to retrieve the maximum file descriptor number	155	# Use the getrlimit method to retrieve the maximum file descriptor number
156	# that can be opened by this process. If there is not limit on the	156	# that can be opened by this process. If there is not limit on the
157	# resource, use the default value.	157	# resource, use the default value.
158	#	158	#
159	import resource # Resource usage information.	159	import resource # Resource usage information.
160	maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]	160	maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
161	if (maxfd == resource.RLIM_INFINITY):	161	if (maxfd == resource.RLIM_INFINITY):
162	maxfd = MAXFD	162	maxfd = MAXFD
163		163
164	# Iterate through and close all file descriptors.	164	# Iterate through and close all file descriptors.
165	for fd in range(0, maxfd):	165	for fd in range(0, maxfd):
166	try:	166	try:
167	os.close(fd)	167	os.close(fd)
168	except (KeyboardInterrupt, SystemExit):	168	except (KeyboardInterrupt, SystemExit):
169	raise	169	raise
170	except OSError: # ERROR, fd wasn't open to begin with (ignored)	170	except OSError: # ERROR, fd wasn't open to begin with (ignored)
171	pass	171	pass
172		172
173	# Redirect the standard I/O file descriptors to the specified file. Since	173	# Redirect the standard I/O file descriptors to the specified file. Since
174	# the daemon has no controlling terminal, most daemons redirect stdin,	174	# the daemon has no controlling terminal, most daemons redirect stdin,
175	# stdout, and stderr to /dev/null. This is done to prevent side-effects	175	# stdout, and stderr to /dev/null. This is done to prevent side-effects
176	# from reads and writes to the standard I/O file descriptors.	176	# from reads and writes to the standard I/O file descriptors.
177		177
178	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDONLY) # stdin	178	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDONLY) # stdin
179	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDWR) # stdout	179	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDWR) # stdout
180	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDWR) # stderr	180	os.open(Settings.Settings["LOGPATH"], os.O_CREAT\|os.O_APPEND\|os.O_RDWR) # stderr
181		181
182	# This call to open is guaranteed to return the lowest file descriptor,	182	# This call to open is guaranteed to return the lowest file descriptor,
183	# which will be 0 (stdin), since it was closed above.	183	# which will be 0 (stdin), since it was closed above.
184	#os.open(REDIRECT_TO, os.O_RDWR) # standard input (0)	184	#os.open(REDIRECT_TO, os.O_RDWR) # standard input (0)
185		185
186	# Duplicate standard input to standard output and standard error.	186	# Duplicate standard input to standard output and standard error.
187	#os.dup2(0, 1) # standard output (1)	187	#os.dup2(0, 1) # standard output (1)
188	#os.dup2(0, 2) # standard error (2)	188	#os.dup2(0, 2) # standard error (2)
189		189
190	return(0)	190	return(0)
191		191